Die fetale/neonatale Alloimmun-Thrombozytopenie (FNAIT)

Abstract

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is characterized by an incompatibility between maternal antibodies and paternally inherited fetal platelet antigens. Although it differs from fetal Rhesus disease, FNAIT also affects first pregnancies. The most severe fetal complication is intracerebral hemorrhage, which occurs in 14 % of affected fetuses. The most common causative antigen is HPA-1a, followed by HPA-5, HPA-15 and HPA-3. The diagnosis of FNAIT requires the presence of (i) fetal thrombocytopenia and (ii) maternal antibodies, corresponding to a paternal antigen. Therapy can be instituted from 18 weeks onward. Treatment strategies include maternally administered intravenous immunoglobulin infusion (IVIG) without or with steroids and fetal platelet transfusions. Intrauterine transfusion can clearly raise fetal platelets, but must be administered repeatedly (up to weekly) and carries a cumulative complication risk from the repeated fetal procedures. Therefore non-invasive methods have been sought. Delivery usually is done by cesarean section unless a safe fetal platelet count is documented. All therapies should be performed using an interdisciplinary approach.